Magnifying spectacles have their principal application in those surgical areas in which an operating microscope cannot be used for technical and anatomical reasons but in which unaided human vision is inadequate to enable the surgeon to see adequately the field of surgery. This problem arises commonly in vascular surgery and neurosurgery. It is frequently desirable or even necessary during an operation to alter the working distance, i.e., the distance between the eyes and the operating point and/or the magnification factor with which the operating point is being observed. Known operating or magnifying spectacles either do not satisfy this requirement, or they do so only incompletely. No magnifying spectacles are known from the prior art which have means for automatically altering the focal length with parallax compensation and also means for altering or adjusting the magnification factor. Reference is made in this connection to the following documents which are briefly discussed below.
______________________________________ D1 AT E98 782B D2 US 4 865 438 D3 US 4 807 985 D4 DE 37 20 190 D5 US 5 078 469 ______________________________________
Document D1 relates to magnifying spectacles for surgical purposes with a device for automatically altering the focal length of the spectacles and the focal length adjustment is mechanically coupled to a device for automatically matching the parallax to the current focal length. The determination of the current distance of the spectacles to the subject is made by ultrasound or light sensors.
Document D2 also relates to magnifying spectacles, particularly for surgical purposes, whose focal length is automatically adjusted to the current distance of the subject. The distance determination is accomplished as in D1.
Documents D3 and D4 disclose telescopic spectacles for people with impaired vision for viewing near and remote objects. The spectacles in accordance with D3 have devices for automatically matching the focal length and for matching the angle of inclination to the position of the head of the user. Spectacles in accordance with D4 have manually operable devices for altering the focal length (slide-in prisms) and for parallax compensation (actuating lever).
Magnifying spectacles for surgical purposes disclosed in document D5 are equipped with a video camera which has a zoom lens system and permits not only photographic recordal but also the transfer of the field of view of the operator, which is illuminated by means of a fiber optic system, to remote stations.
When one is using fixed focus spectacles in certain situations, such as work in the stomach cavity, the user must move his head closer to the open stomach wall due to the requirement for a constant spacing between the eyes and the working field and thus moves, on the one hand, into an ergonomically undesirable body attitude and, on the other hand, obstructs the field of view of assisting doctors with his head, thus making the provision of assistance more difficult. Magnifying spectacles with manually adjustable focus also do not help in this connection because, for sterility reasons, the focus can only be adjusted before, but not during, an operation.